Optical waveguide glass fibers have become an increasingly important long-distance communications medium, and their commercial use for communications over intermediate and short distances is increasing as well. Manufacture of optical waveguide fibers typically is by drawing from a preform as may be made in a number of ways; in this respect see, e.g., U.S. Pat. No. 4,217,027, issued Aug. 12, 1980 to J. B. MacChesney et al. For the sake of mechanical protection, drawn fibers typically are provided with a plastic coating, and coated fibers may be assembled into strands and cables.
In the construction of long-distance communications facilities, special attention is due the optical and physical interconnection of lengths of fiber. In this respect, heat fusion splicing has been developed as reported, e.g., by J. T. Krause et al., "Tensile Strengths &gt;4 GPa for Light Guide Fusion Splices", Electronics Letters, Vol. 17 (1981), pp. 812-813. There, the choice of processing conditions is strongly influenced by considerations of tensile strength of a resulting spliced fiber, this in view of considerable tensile forces as may be applied in the course of cable installation, e.g., by pulling through ducts or by laying at sea.
Heat fusion splicing typically involves the use of a torch producing a flame which results upon the combustion of gases such as, e.g., hydrogen or ammonia. And, of course, such a flame can be used for high-temperature processing for purposes other than splicing. For example, flame processing can be used to facilitate drawing of a fiber to a smaller diameter, for side-by-side fusing of fibers as, e.g., in the manufacture of optical couplers and taps, as well as for the sake of modifying dopant profile. With respect to dopant profile modification see, e.g., J. T. Krause et al., "Splice Loss of Single-mode Fiber as Related to Fusion Time, Temperature, and Index Profile Alteration", IOOC-ECOC '85, Technical Digest, Vol. 1, Istituto Internazionale delle Comunicazioni, 1985; pp. 629-631. And, with respect to diameter reduction, see, e.g., U.S. Pat. No. 3,825,319, issued July 23, 1974 to J. S. Cook et al.
While flame processing with chlorine addition has been found to result in highest tensile strength in a processed fiber, there remain circumstances under which the use of chlorine is inadvisable, e.g., on the basis of safety or environmental considerations. Accordingly, there is demand for effective flame processing in the absence of chlorine.